1. Field of the Invention
The present invention relates to a manufacturing method for Li composite oxides which are applied as electrode materials in Li ion batteries.
The present application is based on Japanese patent applications (Japanese Patent Application No. HEI 9-71604, Japanese Patent Application No. HEI 9-347787), and the contents of the Japanese applications incorporate a portion of the present specification.
2. Related Art
Conventionally, Li composite oxides used as electrode materials in Li ion batteries, such as LiMn composite oxides or LiNi composite oxides or the like, were produced by a method termed the fusion impregnation method.
For example, an LiMn composite oxide having an Li.sub.0.33 MnO.sub.4 composition is produced by the following method. First, lithium nitrate (LiNO.sub.3) and manganese (IV) oxide (MnO.sub.2) having a surface area of 20 m.sup.2 /g or more are weighed out and mixed so as to achieve a ratio of Li:Mn=1:3, and a raw material mixture is thus created. Next, this raw material mixture is heated for approximately 5 hours at a temperature above the melting point of LiNO.sub.3 of 260.degree. C. (commonly, at approximately 300.degree. C.). By means of this heating, the LiNO.sub.3 in the molten raw material mixture is impregnated in the MnO.sub.2. After this heating, the raw material mixture is termed the reaction mixture. This reaction mixture is heated for a period of 10 hours in a nitrogen atmosphere at a temperature of 350.degree. C., and thereby NO.sub.x gas is released from the reaction mixture, and Li.sub.0.33 MnO.sub.4 is obtained.
Furthermore, an LiMn composite oxide having an LiMn.sub.2 O.sub.4 composition is produced in the following manner. First, manganese (IV) oxide and lithium nitrate are mixed so as to obtain a ratio Li:Mn=1:2, and a raw material mixture is thus produced. Next, in the same manner as described above, the raw material mixture is heated, and the LiNO.sub.3 present in the raw material mixture is impregnated in the MnO.sub.2. Next, the reaction mixture obtained is heated for a period of ten hours in a nitrogen atmosphere at a temperature of 650.degree. C., and by means of the release of NO.sub.x gas, LiMn.sub.2 O.sub.4 is obtained.
Furthermore, other Li composite oxides are produced by the following method. First, an Li oxide and a composite oxide powder of Co, Ni, Mn or the like, or a carbonate of Co, Ni, Mn, or the like, are mixed at a predetermined molar ratio to produce a raw material mixture. Next, this raw material mixture is heated to approximately 700.degree. C. The reaction mixture obtained is again mixed and subjected to heat treatment, then a predetermined Li composite oxide is obtained.
In the method employing LiNO.sub.3 as the raw material as described above, NO.sub.x gas is emitted in the final stage of the manufacturing process. In this method, large scale disposal devices are required in order to remove the NO.sub.x gas, and thus the large scale production of Li composite oxides was extremely difficult. Furthermore, it was necessary to employ Mn oxides having a large surface area as the other raw material.
Furthermore, in the method which Li oxides are used as the raw material, it was necessary to repeatedly conduct heat treatment at high temperatures. However, since Li tends to evaporate at high temperatures, it was difficult to obtain Li composite oxides having the predetermined composition. Furthermore, defects were produced in the crystalline structure of the Li composite oxides obtained, and there were thus undesirable large variations in the electrical properties thereof.